Malignant lues is a rare form of secondary syphilis mostly associated with HIV infection. It is an uncommon presentation of syphilis even rarer in immunocompetent patients. We present the case of a 57-year-old homosexual man referred to our department due to a 4-month history of a disseminated, slightly painful, nodular-ulcerative cutaneous eruption associated with low-grade fever, malaise and aesthenia. Regarding the clinical features and serological and histopathological findings, the diagnosis of syphilis maligna was assumed. Serology for HIV was repeatedly negative. This case is interesting, not only because a very uncommon form of secondary syphilis was identified but also for being diagnosed in an immunocompetent patient. Lack of awareness of this type of presentation delays the diagnosis and treatment, leading to an increase in morbidity and spread of infection.